The present invention relates to a cylinder head gasket sandwiched between a cylinder head and a cylinder block of an open-deck type engine and sealing therebetween.
The cylinder head gasket is sandwiched between engine members such as the cylinder head and the cylinder block (cylinder body) and the like of an automobile engine and tightened by head bolts, thereby sealing fluid such as combustion gas, oil, coolant water and the like.
On the other hand, if the engines are distinguished based on a type of the cylinder block, there are a closed-type engine which does not have a coolant water channel on a contact surface between the cylinder block and the cylinder head, and an open-deck type engine wherein the contact surface between the cylinder block and the cylinder head is open to be used as a coolant liquid channel. As shown in FIG. 12, the open-deck type engine includes a coolant liquid channel (water jacket) 54 near the cylinder head of an engine block 52, so that it has an advantage in terms of a cooling performance and reduction in weight. Furthermore, since there is an opening, it can be easily manufactured.
Regarding the cylinder head gasket for the open-deck type engine, a metal gasket has been proposed (for example, refer to Japanese Patent Publication (TOKKAI) No. H10-281290). The metal gasket provides a grommet along the inner periphery of a cylinder hole in a plate which covers both a cylindrical portion of the cylinder block and an outer wall portion forming the outside of the coolant water channel; seals the combustion gas of a cylinder bore at the thickest portion of the grommet formed in the inner side of a cylinder sleeve; and also seals the coolant water by a step bead formed on both sides of the coolant water channel.
In this cylinder head, the step bead is provided for sealing the coolant water between the coolant water channel and the cylinder bore. However, a position of an angular portion of the step bead is located on the inner peripheral side of a wall surface (the outer wall surface of the cylindrical portion) of the coolant water channel, and the coolant water contacts the upper surface of a cylinder liner (cylindrical portion). Therefore, an electric etching occurs at the contact surface of the cylinder block due to contact with liquid coolant water containing anti-freezing liquid (LLC) to aluminum alloy, so that the sealing performance of the portion tends to be deteriorated.
If the sealing performance between the cylinder bore and the coolant water channel is deteriorated, the combustion gas enters the coolant water channel, and a circulation of the coolant water is hindered. This causes a major engine trouble. Therefore, sealing a cylinder bore side becomes more important than the sealing of a bolt hole side or an external portion side. In order to prevent the electric etching, it is important to prevent a coolant liquid in the coolant liquid channel from directly contacting the upper surface of the cylinder liner. Conventional technology was not good enough to prevent the electric etching caused by the contact of the coolant water with anti-freezing liquid, and did not focus on the relationship with the coolant water channel, even though a seal line is provided. As a result, the contact of the coolant liquid to the upper surface of the cylinder liner could not be fully prevented.
The present invention has been made in order to solve the problems described above. An object of the present invention is to provide a cylinder head gasket for the open-deck type engine, and prevent the electric etching, which occurs due to the contact of the coolant water with anti-freezing liquid on the upper surface of the cylindrical portion forming the cylinder bore, and improve the sealing performance.
Further objects and advantages of the invention will be apparent from the following description of the invention.